Conventionally, there is an antenna duplexer which is used by switching a single antenna by transmission signals and reception signals having different frequencies. This antenna duplexer includes a high frequency switch circuit that supplies transmission signals to the antenna, and a band limit filter that outputs reception signals output from the antenna to a predetermined reception circuit. In the band limit filter, frequency characteristics are selected such that the frequency band of the transmission signal is suppressed, and the reflected wave generated at the input terminal is maintained at a predetermined phase such that the impedance becomes high at the frequency band of the transmission signal.
Furthermore, the antenna duplexer switches the contact point of the switch circuit, and switches the transistor to an ON state at the time of transmission or switches the transistor to an ON state at the time of reception, and selectively connects the single antenna to the transmitting circuit and the receiving circuit (see, for example, Patent Document 1).    Patent Document 1: Japanese Laid-Open Patent Publication No. H06-291696
Incidentally, a conventional antenna duplexer includes a switch in the transmission path of the transmission signal or the reception signal, and therefore a loss occurs when the transmission signal or the reception signal is transmitted to the switch.